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FAST II: Algorithms and Performance

FAST II: Algorithms and Performance. Cheng Jin David Wei Steven Low http://netlab.caltech.edu. Topics. Design Issues FAST (sc2002 version) Window Pacing Experimental Results. Design Issues. Raj Jain ’ s “ Three questions that a congestion control algorithm should answer ” :

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FAST II: Algorithms and Performance

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  1. FAST II: Algorithms and Performance Cheng Jin David Wei Steven Low http://netlab.caltech.edu

  2. Topics • Design Issues • FAST (sc2002 version) • Window Pacing • Experimental Results

  3. Design Issues Raj Jain’s “Three questions that a congestion control algorithm should answer”: • Decision Frequency (Timescale) • Decision function • How to Increase/Decrease Window

  4. How Frequent? • Timescale of a congestion control algorithm New Reno:

  5. Decision Function

  6. Decision Function using Binary Signal

  7. Congestion Signal • Loss • Delay • ECN

  8. Increase/Decrease Function • Under synchronization assumption (Chui and Jain):

  9. Congestion Control Algorithms

  10. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  11. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  12. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  13. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  14. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  15. FAST (sc2002) Algorithm Do the following every other RTT: per acknowledgment: • Calculation: • Action: • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1 No more aggressive than Rate Halving No more aggressive than Slow Start

  16. Results on Convergence Under synchronization model: • Single link identical sources: converge • Single link heterogeneous sources: bounded by converging sequences • General case: Contraction mapping

  17. Simulation with Matlab pkt/ms • baseRTT: 550ms,600ms,650ms,700ms,750ms • Alpha=500 pkt • C=5000/12 pkt/ms pkt/ms pkt pkt

  18. Simulation with Matlab ms pkt • baseRTT: 550ms,600ms,650ms,700ms,750ms • Alpha=500 • C=5000/12 pkt/ms

  19. Window Pacing

  20. Pacing Why Pacing? • Eliminate “noise” of packet loss due to burstiness (for loss-based algorithms). • Eliminate “noise” of queuing delay due to burstiness (for delay-based algorithms). • Pacing can make the behavior of TCP more fluid-like Why not pacing?

  21. Window Pacing Over one RTT: • Action (each acknowledgment): • If w(t)>w*: w(t)=w(t)-1 • If w(t)<w*: w(t)=w(t)+1

  22. Time-Based Window Pacing cwnd increments are scheduled at fixed intervals. data data ack k k k k k k (Cheng Jin, Caltech)

  23. Event-Based Pacing Detect sufficiently large gap between consecutive bursts and delay cwnd increment until the end of each such burst. (Cheng Jin, Caltech)

  24. Implementing Pacing • Using Intel x86 cycle counter for high resolution • Combination of time-based and event-based pacing • Time-based pacing is supported only for single TCP stream in a single machine • Event-based pacing can support multiple TCP streams in a single machine (Cheng Jin, Caltech)

  25. Experiments • SC2002 • Dummynet • Internet2 • Summary

  26. SC2002 Network OC48 OC192 (Sylvain Ravot, Caltech)

  27. FAST BMPS 10 #flows 9 Geneva-Sunnyvale 7 FAST 2 Baltimore-Sunnyvale FAST • Standard MTU • Throughput averaged over > 1hr 1 Internet2 Land Speed Record 2 1 (Steven Low, Caltech)

  28. Dummynet Testbed@ Netlab, Caltech

  29. Static throughput Dynamic sharing on Dummynet • capacity = 800Mbps • Delay = 50 - 200ms • # flows: 1 - 10 • iperf throughput • Linux 2.4 (HSTCP: UCL)

  30. Static throughput

  31. Dynamic Sharing HSTCP FAST • Fairness Problem Scalable Linux

  32. queue HSTCP FAST Linux loss throughput Linux Scalable HSTCP STCP HSTCP

  33. Dynamic Sharing HSTCP FAST Scalable Linux

  34. Abilene Testing U Washington PSC Caltech GaTech

  35. Abilene Testing 100Mbps Test: Caltech->Gatech • Duration: 120 second • Base RTT: 46ms • UDP blast: every 20 seconds for 5 seconds per blast RTT (us) Cwnd (Cheng Jin, Caltech)

  36. Performance Metrics • Aggregate Average Goodput • Fairness: Jain’s index • Stability: • Responsiveness:

  37. Aggregate throughput Dummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts

  38. HSTCP ~ Reno Jain’sindex Fairness Dummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts

  39. Stability Dummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts

  40. Responsiveness Dummynet: cap = 800Mbps; delay = 50-200ms; #flows = 1-14; 29 expts

  41. Future Works • Congestion Window Control Algorithm: Stability with delay • Synchronization Model • Burstiness Control: Modeling, Measurement • Testing: Experiments in production networks

  42. Questions? Thanks

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